Why newborn babies can't walk

(PhysOrg.com) -- The first steps of an infant is a real milestone in the development of all mammals including humans, but little is known about why some animals can walk soon after birth, while others need months, or in the case of humans, a year or so, to take those first steps. Now a new study by scientists in Sweden has shed light on the mystery, finding that the time it takes for all mammals to start walking closely correlates with the size of their adult brains.

The researchers from Lund University, led by neurophysiologist Martin Garwicz, found that motor development milestones in rats and ferrets, such as crawling and walking, followed the same timetable but at different rates, being faster for rats. The team then wondered if similar results would be found for other mammals.

They used a multiple-regression model to study the time between conception and walking for 24 mammal species, including sheep, chimpanzees, guinea pigs, camels, and aardvarks. They then analyzed these results against variables such as gestation time, adult body size, and the mass of the adult brain. When the time is measured from conception rather than from birth, the pattern became clear.

Their results, reported in the Proceedings of the National Academy of Sciences (PNAS) in the U.S. this week indicate that the mass of the adult brain accounts for 94 percent of the variance between species in the time from conception to walking, so mammals with larger brains, such as humans, take longer to master walking than species with smaller brains.

A further 3.8% of the variance could be explained by the differences in functional limb anatomy in the different species, or in other words, whether the species walks with heels on the ground or on its toes, like horses and cats. Those that walk on the heels (like humans) take the longest time to learn to walk, which the scientists thought might also be related to the brain since this kind of walking is more complex and probably takes more brain power.

Garwicz said the results indicate that similar neuronal mechanisms are activated at a similar relative point in time during brain development of the different species.

One remarkable result of the research is that the model of the walking time's relationship to adult brain mass for the other 23 species leads to an almost perfect prediction of when humans will begin to walk. Garwicz said that we are not an exceptional species in this respect and we start walking at exactly the time predicted from studying the other mammals.

The effect of gestation and the birth brain mass were also analyzed and found to correlate with walking time for most of the animals studied, but not for humans, and the scientists believe this is because humans spend a much smaller percentage of development time in the uterus, and more of the brain mass is developed after birth than it is in many of the other species studied.

Animals such as horses also fit the model of adult brain mass/walking time even though newborn horses walk almost immediately after birth, because the model takes the walking time from conception and not from birth, and horses have a long gestation period.

The researchers said the timing of acquisition of motor skills such as walking seems to have been highly conserved in the evolution of mammals, because the ancestors of some of the species in the study "diverged in phylogenesis as long as 100 million years ago." This would mean that fundamental patterns of early human development may have evolved before the evolution of primates.

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User comments : 16

This would explain why those of African descent, on average, learn to walk before Whites and Whites before Orientals. This correlation, between physical maturity,has been observed by others. A similiar correlation exists between the averge age puberty hits as well.

so mammals with larger brains, such as humans, take longer to master walking than species with smaller brains.

Ok then explain why horses have their legs under themselves prior to dogs but after elephants?

The only way this works is if you involve the conception period, which is always longer for larger animals.

The reason why it takes so long to learn to walk is a matter of motor coordination and average dispersal of weight throughout the body. It's easy to point ot humans and say, "ah ha! It's because our brain is larger". This is both true and untrue. Yes, it's because our brain is larger, but most likely directly due to how large and heavy our upper body is compared to our lower body. This also explains why you see similar lags in dexterity and coordination development in other primates.

Walking on two legs is obviously harder than walking on four otherwise babies would never crawl.

I could just be culturally sensitive ... but Otto you are suggesting that blacks have the smallest adult brains , followed by cuacaziods and mongoloids.

I dissagree with that assesment, humans in general start walking about the same time. You are also suggesting that race determines entry into puberty which is flawed as well.

The difference in entry to puberty in the US across races is more closly linked to socio economic level coupled with diet. the poorer you are the more likely you are to injest a lot of food that contains hormones, and perservatives that have pushed a girls initial menstration from 13-14 down to 9-10 in the US.

@Velanarris --- i agree a weigth factor has to be involved becasue larger / overweight human babies learn to walk ALOT faster than smaller children

the poorer you are the more likely you are to injest a lot of food that contains hormones, and perservatives that have pushed a girls initial menstration from 13-14 down to 9-10 in the US.

You do realize that's an old wives' tale. The amount of hormones in our food has been the same with or without the addition of GH and GM.

The reason why humans enter puberty earlier is because we're more well fed than we used to be. We carry more weight than we used to and as such our body sees our life as being in a "time of plenty" so earlier and earlier chemical procreative signals are sent. It has nothing to do with hormones otherwise we would have never seen it. Plants produce just as many hormones as we inject into animals, in some cases they produce far more.

Velanarris, the start of menstration is known to be affected by the absence of a father figure in a young girls life http://en.wikiped...menarche Given the increasing rates of divorce, single mothers etc, this could possibly account for the observed changes in the start of menstration age

Velanarris, the start of menstration is known to be affected by the absence of a father figure in a young girls life http://en.wikiped...menarche Given the increasing rates of divorce, single mothers etc, this could possibly account for the observed changes in the start of menstration age

That is a lesser causative than nutrition.

They've done long term surveys of people in the developing world and the results have lent strong causative evidence to nutrition and overall fat content being the main driver of human maturity onset.

@Velanarris: excessive weight may be an effect of chemical precursors found in our diet today that weren't there 50 years ago. Specifically, BPA. Kembra Howdeshell and Frederick vom Saal recently published a study. What resulted were findings that included an earlier onset of puberty and an increase in body weight after birth. What may be more important was the reaction was also related to natural levels of estrogen: the more you have the more you are affected.

Finally, and this is likely the key here, it seems to program the body for weight gain in the uterus, and doesn't necessarily affect adults. That would explain the slow increase in average weight and slow decrease in average age on puberty onset over the last 50 years of BPA use.

Ok, firstly I'd like to point out that although the world does benifit from studies like these, most of this stuff is just someones theory or guesswork on evolution... If anyone could predict what the world, or universe, was like "millions" and "billions" of years ago, they sure as hell wouldn't be part of civillian life as they would be "super-human". A huge per ent of modern findings are "theories" which scientists themselves say may not be accurate...Now secondly, why does science look for complicated answers rather than just the simple ones..?? Could it not just be possible that humans actually take longer to start walking because we don't HAVE to start walking as soon as horses, rats and so on... WHY would modern humans have to start walking early..?? We have no "predators", we have saftey, warmth, food and most importantly other humans to take care of us... (comment continued, please read next comment.....

Where is the need for us to start walking the day we are born, or even the need for us to walk one, two or even three months after birth... We learn these things in time giving our brains more time do develop into the most powerful thing on this planet...To give an exapmle. Some of the most intelligent animals are not those that are left to fend for themselves after birth but those animals who are taken care of (albeit on a much more basic level), chipmanzees are taught their survival skills in the wild for around 8 or 9 years...during this time the young chimpanzees do not have to "worry" about food and other such things that the adult chimpanzees do for them in their infancy. When was the last time you saw a new born chimpanzee swinging from tree to tree? And when was the last time you saw a new born chimpanzee cling to the back/belly of an adult chimpanzee? They too have no instant "NEED" to learn this, although this period is much much shorter as they have less "protection"...

Balderdash!! The real reason newborns humans are unable to walk after birth is because of the last link in our evolution. Its what gave us our naked skin, subcutaneous fat layer, and even our ability to speak. Its called aquatic ape theory, and its our true evolutionary lineage.Check out my videos to see more. I found the elusive Clovis comet impact crater that just may reveal how it shaped our destiny as a species. I am just an amateur so please feel free to comment constructively!!http://www.youtub...Gy8TIinIhttp://www.youtub...JZJghnSIhttp://www.youtub...0L23Ughc

Bob Kob: Wouldn't that only make sense if we were using the normal instinct patterns of a different species? As we're humans, though, and presumably evolution has provided us with human "programming," so to speak, we're comfortable enough in our own bodies to not need advanced training.

I'm surprised that there seems to be so much disagreement with this study; I mean, they established a pretty strong correlation, it seems (94%? Goodness gracious), so...well, seems pretty robust to me, unless that's deceptive and what they're comparing is strongly correlated with some other feature that's the REAL cause.

@OttoI could just be culturally sensitive ... but Otto you are suggesting that blacks have the smallest adult brains , followed by cuacaziods and mongoloids.

This is the problem with you and most of you non-scientists/engineers on Physorg,you either 'believe' or 'don't believe' in a whole range of issues due to a personal belief system. What does believing have to do with anything? It is an easily confirmable fact that has been known for at least half a century that brain size varies between peoples. That is the reality, deal with it. The average age of the onset of puberty, sexual activity, and yes, walking, also follow the same correlation. Just to piss off you socially conscious lemmings I will add that IQ also follows the same correlation. Of course there are a whole other range of factors that have an influence.There are plenty of papers out there that back up these assertions. If one doesn't want to accept reality because of some holy belief system,well,your loss.

The doctor that attended the birth of my first child ... mentioned that the time it takes to walk is very short - but the shape of a baby, with an offset centre of balance determines that a small child just has to wait until maturation shifts some weight centres (if that is a term) around.

The reason girls in particular hit puberty faster is because of the birth control hormones that accumulate in the water supply. When a woman is on "the pill" her body doesn't completely absorb the entire amount of hormones in the pill. These unabsorbed hormones are passed out of the body and into the sewage system. The sewage water is then converted into drinking water, which is consumed by people, by a process that does not seek to remove the birth control hormone molecules from the water supply. The internal production of estrogen in girls is what causes puberty and artificial introduction (via tainted drinking water) of estrogen earlier than when production would naturally take place causes the body to start puberty earlier.

A bit further off subject: another major milestone in human development is the ability to know the difference between pink and purple. Believe it or not..

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